Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/001—Heat treatment of ferrous alloys containing Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/005—Heat treatment of ferrous alloys containing Mn
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/008—Heat treatment of ferrous alloys containing Si
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0236—Cold rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0273—Final recrystallisation annealing
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/007—Ferrous alloys, e.g. steel alloys containing silver
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys

Definitions

• the present disclosure relates to steel materials and automobile parts.
• steel materials used in automobiles are required to have both high strength and high ductility that can be molded according to the shape of the part in order to reduce the weight of the car body and improve safety performance.
• high corrosion resistance is also required to extend the service life.
• AHSS Advanced High Strength Steel
• First generation AHSS represented by TRIP (Transformation-Induced Plasticity) steel
• TRIP Transformation-Induced Plasticity
• second-generation AHSS typified by high-Mn steel
• high-Mn steel has an excellent balance of strength and ductility, but is not widely used, partly due to its high Mn content.
• Patent Document 1 states that ⁇ Mn: 3 to 8%, Al: 2 to 4%, Si: 0.1 to 0.2%, C: 0.3 to 0.8%, and the remainder iron and impurities.
• a steel sheet containing a ferrite phase, a bainite phase, an austenite phase, a martensitic phase and a process for providing the steel sheet are disclosed.
• Patent Document 2 states, ⁇ C: 0.1 to 0.4%, Mn: 1 to 3%, Si: 1 to 2%, Ti: 0.1 to 0.2%, and the balance is iron and impurities.
• a steel sheet and a process for providing a steel sheet having a composition comprising a ferrite phase, a bainite phase, an austenite phase, and a martensitic phase are disclosed.
• Patent Document 3 states, “C: 0.12 to 0.24%, Mn: 0.8 to 2.1%, Si: 0.4 to 1.1%, Cr: 0.8 to 1.5%. , Al: 0.05-0.3%, Mo: 0.05-0.25%, Nb: 0.018-0.035%, Ti: 0.01-0.1%, S: max. 008%, P: up to 0.025%, N: up to 0.005%” is disclosed.
• Patent Document 1 Japanese Patent Application Publication No. 2016-141888 Patent Document 2: Japanese Patent Application Publication No. 2016-223003 Patent Document 3: Japanese Patent Publication No. 2020-514544
• Mn is contained in an amount of 0.8 to 8%, and the structure is formed with complex irregular phases (ferrite, austenite, martensite, bainite, etc.) to obtain a balance of strength, ductility, and strength-ductility. ing.
• an object of the present disclosure is to provide a steel material that has high strength, high ductility, and high strength-ductility balance, and also has high corrosion resistance and high manufacturability at a level that exceeds the current third generation AHSS. .
• the means for solving the above problem includes the following aspects.
• ⁇ 2> The steel material according to ⁇ 1>, wherein the average chemical composition of the steel material satisfies the following formula A.
• Formula A C+Mn/6+Si/24+Ni/40+Cr/5 ⁇ 1.4 (In formula A, each element symbol indicates the content (mass%) of the corresponding element.)
• ⁇ 3> The steel material according to ⁇ 1> or ⁇ 2>, wherein the average area ratio of the austenite phase is in the range of 20 to 80%.
• the ordered phase includes a DO3 type ordered phase, and the ratio of the DO3 type ordered phase to all ordered phases ([DO3 type ordered phase]/[all ordered phases]) determined by X-ray diffraction is expressed by the following formula B.
• each element symbol ⁇ indicates the content of the corresponding element in the austenite phase (mass% ).
• ⁇ 7> The steel material according to any one of ⁇ 1> to ⁇ 6>, wherein the average grain size of the ordered phase is 10.00 ⁇ m or less.
• ⁇ 8> The steel material according to any one of ⁇ 1> to ⁇ 7>, wherein the ordered phase includes an antiphase boundary.
• ⁇ 9> The steel material according to any one of ⁇ 1> to ⁇ 8>, wherein the product of tensile strength and total elongation is 30,000 MPa% or more.
• ⁇ 10> The steel material according to any one of ⁇ 1> to ⁇ 9>, having a tensile strength of 1250 MPa or more.
• ⁇ 11> An automobile part comprising the steel material according to any one of ⁇ 1> to ⁇ 10>.
• FIG. 1 is an example of an optical micrograph of the metal structure of the steel material of the present disclosure of test number 35 after hot rolling annealing and before finish annealing (magnification: 500x, white part is ⁇ phase, gray part is regular phase) .
• FIG. 2 is an example of an optical micrograph of the metal structure of the steel material of the present disclosure of test number 36 (magnification: 500 times, white part is ⁇ phase, gray part is regular phase).
• the steel material of the present disclosure has a predetermined average chemical composition and a metal structure including an austenite phase and an ordered phase.
• the steel material of the present disclosure has high strength, high ductility, and high strength-ductility balance, and has high corrosion resistance and high manufacturability at a level higher than that of the current third generation AHSS.
• the steel material of the present disclosure was discovered based on the following findings.
• the main chemical composition of the steel material is to contain 18.00 to 36.00% Ni and 5.50 to 12.00% Si, and the amount of arbitrary elements other than Ni and Si, which will be described later, is below a predetermined amount (especially By setting the amount of Al and the amount of Mn to a predetermined amount or less, a metal structure containing a ⁇ phase and an ordered phase is obtained.
• the strength, ductility, and strength-ductility balance of the steel material are increased.
• the amount of arbitrary elements other than Ni and Si, which will be described later becomes excessive, the strength or ductility will deteriorate.
• the corrosion resistance of the steel material also increases. Generally, when 5.50 to 12.00% of Si is contained, the steel material becomes brittle, making hot working and cold working difficult.
• the steel material of the present disclosure has high strength, high ductility, and high strength-ductility balance, and has high corrosion resistance and high manufacturability at a level that exceeds the current third generation AHSS. was discovered.
• Ni contributes to improving ductility and strength-ductility balance.
• Ni is a gamma stabilizing element, and its inclusion in the steel material stabilizes the gamma phase.
• the ⁇ phase has relatively excellent ductility compared to the ordered phase. By including the ⁇ phase in the steel material, the balance between ductility and strength-ductility is improved. Such effects are noticeable when the Ni content is 18.00% or more. If the amount of Ni is too small, the stability of the ⁇ phase will not be sufficient, resulting in cracking during the manufacturing process, resulting in insufficient ductility of the steel material and an insufficient balance of strength and ductility.
• the Ni content is 18.00 to 36.00%.
• the lower limit of the Ni content is preferably 20.00%, more preferably 22.00%.
• the upper limit of the Ni content is preferably 32.00%, more preferably 30.00%.
• Si contributes to improving strength, strength-ductility balance, and corrosion resistance.
• Fe contains a large amount of Si
• the ⁇ phase becomes regular.
• a steel material is composed of a metal structure consisting only of an ordered phase in which the ⁇ phase is ordered
• the steel material becomes brittle and is difficult to be used industrially.
• the steel contains both the ⁇ phase and the ordered phase
• the ordered phase is harder than the ⁇ phase and contributes to improving strength.
• a protective layer containing Si oxide which has excellent corrosion resistance, is formed on the surface of the steel material. Therefore, the inclusion of Si is effective in improving corrosion resistance.
• the Si content is 5.50% or more. If the amount of Si is too small, the ⁇ phase will not be sufficiently ordered, resulting in insufficient formation of ordered phases, resulting in insufficient strength of the steel material and insufficient strength-ductility balance. In addition, the formation of a Si oxide layer that functions as a protective layer on the surface of the steel material becomes insufficient, and the improvement in corrosion resistance also becomes insufficient. If the content of Si is too high, cracks will occur during the manufacturing process, the ductility of the steel material will be insufficient, and the strength-ductility balance will also be insufficient. Therefore, the Si content is 5.50 to 12.00%. The lower limit of the Si content is preferably 6.50%, more preferably 8.00%. The upper limit of the Si content is preferably 10.00%, more preferably 9.50%.
• Cu is an optional element.
• Cu like Ni, has the effect of stabilizing the ⁇ phase and improving the balance of ductility and strength-ductility. Compared to Ni, Cu has a smaller amount of atoms that can be solid-solubilized in the ⁇ phase, and excessive Cu content causes Cu precipitation, resulting in a decrease in ductility and manufacturability. Therefore, the Cu content is 0 to 2.00%.
• the lower limit of the Cu content is preferably 0.20%.
• the upper limit of the Cu content is preferably 1.50%.
• Al is an optional element.
• Al like Si, has the effect of regularizing the ⁇ phase and improving the balance between strength and strength-ductility. Note that even if Al is contained, there is no effect of improving corrosion resistance.
• excessive Al content lowers the Si solid solubility limit in the steel material.
• excessive Al content inhibits the formation of ordered phases (specifically, the B2 type ordered phase whose basic chemical composition is FeSi and the DO3 type ordered phase whose basic chemical composition is Fe 3 Si), It also has a negative effect on corrosion resistance. Therefore, the Al content is 0 to 3.000%.
• the lower limit of the Al content is preferably 0.002%, 0.005%, 0.010%, or 0.100%.
• the upper limit of the Al content is preferably 2.700%, 2.000%, 1.500%, or 1.000%.
• Mn is an optional element. Like Ni and Cu, Mn has the effect of stabilizing the ⁇ phase and improving the balance between ductility and strength-ductility. On the other hand, Mn has no particular effect on corrosion resistance, and excessive Mn content results in the formation of MnS, which deteriorates corrosion resistance. Therefore, the Mn content is 0 to 2.00%.
• the lower limit of the Mn content is preferably 0.02%, 0.05%, or 0.10%.
• the upper limit of the Mn content is preferably 1.60%, 1.40%, or 1.00%.
• C is an optional element. Like Ni, C has the effect of stabilizing the ⁇ phase and improving the balance of ductility and strength-ductility. On the other hand, excessive C content promotes the formation of coarse Fe carbides, resulting in cracking during the manufacturing process. Therefore, the C content is set to 0 to 0.100%. Since it is difficult to reduce the C content to 0%, the lower limit of the C content is preferably 0.001%, 0.005%, or 0.010%. The upper limit of the C content is preferably 0.085%, 0.075%, or 0.060%.
• Cr is an optional element. Cr has the effect of suppressing the occurrence of corrosion starting from inclusions. On the other hand, excessive Cr content causes embrittlement and fracture. Therefore, the Cr content is 0 to 0.40%.
• the lower limit of the Cr content is preferably 0.01%.
• the upper limit of the Cr content is preferably 0.35%.
• P and S are impurities and reduce the toughness of steel materials. Therefore, the contents of P and S are each 0 to 0.200%.
• the content of P and S is preferably as low as possible, but may be 0.001% or more from the viewpoint of cost for removing P and S.
• N and B are optional elements.
• N and B are solid solution strengthening elements and have the effect of contributing to improving strength.
• N and B can also be used to control pinning particles and inclusions.
• excessive N and B content forms unnecessarily large nitrides or borides, which causes a decrease in ductility. Therefore, the N and B contents are each 0 to 0.200%.
• the lower limit of the content of N and B is preferably 0.001% each.
• the upper limit of the content of N and B is preferably 0.150% each.
• Sn, Ge, Ag, Sb and Te 0 to 0.20%> Sn, Ge, Ag, Sb and Te are optional elements. Sn, Ge, Ag, Sb, and Te have the effect of contributing to improving corrosion resistance. On the other hand, excessive content of Sn, Ge, Ag, Sb, and Te causes the material to become brittle and reduce manufacturability. Therefore, the contents of Sn, Ge, Ag, Sb and Te are each 0 to 0.20%.
• the lower limit of the content of Sn, Ge, Ag, Sb and Te is preferably 0.01% each.
• the upper limit of the content of Sn, Ge, Ag, Sb and Te is preferably 0.18% each.
• V, Nb and Ti are optional elements.
• V, Nb, and Ti have the effect of forming carbonitrides and the like to refine crystal grains. Ti also functions as a deoxidizing element.
• excessive content of V, Nb, and Ti causes these elements to solidify and segregate, resulting in a decrease in crack manufacturability during casting and solidification. Therefore, the contents of V, Nb and Ti are each 0 to 0.200%.
• the lower limit of the content of V, Nb and Ti is preferably 0.001% each.
• the upper limit of the content of V, Nb and Ti is preferably 0.080% each.
• Ca and Mg are optional elements.
• Ca and Mg form inclusions such as oxides and sulfides, modify the metal structure of the ingot, and suppress cracking during casting, thereby improving productivity.
• excessive content of Ca and Mg increases the number, size, volume ratio, etc. of inclusions, which causes flaws and cracks during manufacturing. Therefore, the contents of Ca and Mg are each 0 to 0.200%.
• the lower limits of the contents of Ca and Mg are each preferably 0.001%.
• the upper limits of the contents of Ca and Mg are each preferably 0.150%.
• Li, Sr, REM and Zr are optional elements. Li, Sr, REM, and Zr have the effect of contributing to improving oxidation resistance. On the other hand, by containing excessive amounts of Li, Sr, REM, and Zr, the effect of further improving oxidation resistance cannot be obtained, but only increases the raw material cost. Therefore, the contents of Li, Sr, REM and Zr are each 0 to 0.20%.
• the lower limit of the content of Li, Sr, REM, and Zr is each preferably 0.01%.
• the upper limit of the content of Li, Sr, REM, and Zr is preferably 0.18% each.
• REM rare earth element
• Sc and Y and 15 lanthanoid elements, such as La, Ce, and Nd.
• REM is composed of one or more types selected from these rare earth elements, and the content of REM is the total content of rare earth elements.
• Co is an optional element. Co has the effect of contributing to improving toughness. It also has the effect of stabilizing the ⁇ phase. On the other hand, excessive Co content causes deterioration of the corrosion resistance of the ordered phase and deterioration of the toughness of the steel material itself. Therefore, the Co content is 0 to 0.20%, respectively.
• the lower limit of the Co content is preferably 0.01%.
• the upper limit of each Co content is preferably 0.18%.
• Mo, Ta, W, PGM, Au and Re are optional elements. Mo, Ta, W, PGM, Au, and Re have the effect of contributing to improving corrosion resistance. On the other hand, excessive content of Mo, Ta, W, PGM, Au, and Re causes the ductility of the ordered phase to decrease, thereby decreasing the ductility of the steel material itself. Therefore, the contents of Mo, Ta, W, PGM, Au, and Re are each 0 to 0.20%.
• the lower limit of the content of each of Mo, Ta, W, PGM, Au and Re is preferably 0.01%.
• the upper limit of the content of each of Mo, Ta, W, PGM, Au, and Re is preferably 0.19%.
• PGM platinum group elements
• platinum group elements means a general term for six elements: Pt, Pd, Ru, Ir, Os, and Rh.
• PGM is composed of one or more types selected from these platinum group elements, and the content of PGM is the total content of platinum group elements.
• ⁇ In, Ga, Cd and Pb 0 to 0.20%>
• In, Ga, Cd and Pb are optional elements.
• In, Ga, Cd, and Pb have the effect of contributing to improving corrosion resistance.
• excessive content of In, Ga, Cd, and Pb causes a decrease in toughness and deterioration of manufacturability. Therefore, the contents of In, Ga, Cd, and Pb are each 0 to 0.20%.
• the lower limit of the content of In, Ga, Cd, and Pb is each preferably 0.01%.
• the upper limit of the content of In, Ga, Cd and Pb is preferably 0.19% each.
• the balance of the average chemical composition of the steel material of the present disclosure is Fe and impurities.
• Impurities refer to components that are mixed in from raw materials such as ores and scraps and other factors during industrial production of steel materials.
• the upper limit of the "C+Mn/6+Si/24+Ni/40+Cr/5" value (hereinafter also referred to as "A value") in Formula A is more preferably 1.3, and still more preferably 1.0.
• the lower limit of the A value in Formula A is more preferably 0.6, and even more preferably 0.8.
• the metal structure of the steel material of the present disclosure includes a ⁇ phase and an ordered phase.
• Si and Ni are contained in the above ranges, and the amount of any element other than Ni and Si is contained in a predetermined amount or less.
• Fe contains only Si among Ni and Si, although it has excellent corrosion resistance, the steel material itself becomes brittle and processing becomes difficult, making it difficult to use industrially.
• Fe contains only Ni of Ni and Si, sufficient ductility is exhibited, but sufficient strength and strength-ductility balance and corrosion resistance are not exhibited.
• a steel material containing a ⁇ phase and an ordered phase can be obtained by containing both Si and Ni within the above-described appropriate ranges and containing an amount of any element other than Ni and Si in a predetermined amount or less.
• the steel material of the present disclosure preferably has an average area ratio of ⁇ phase of 20 to 80%.
• the steel material of the present disclosure preferably has an average area ratio of ⁇ phase of 20 to 80%.
• the ⁇ phase and the ordered phase it has high strength, high ductility, and high strength ductility balance, and also has high corrosion resistance.
• the average area ratio of the ⁇ phase is within the range of 20 to 80%, the strength, ductility, and strength-ductility balance are further improved.
• the ⁇ phase improves the ductility of the steel material by bearing the strain associated with plastic deformation instead of the hard ordered phase contained in the steel material, and as a result also improves the strength-ductility balance.
• the average area ratio of the ⁇ phase is 20% or more, the ⁇ phase, which is a region responsible for plastic deformation, is moderately present, suppressing the excessive introduction of strain accompanying plastic deformation into the ordered phase, and improving ductility. further improves.
• the average area ratio of the ⁇ phase is 80% or less, while sufficiently improving ductility, the introduction of strain due to plastic deformation to the ordered phase, which contributes to improving strength, is suppressed from becoming too small, and the strength and The strength-ductility balance is further improved. Therefore, in order to optimally exhibit strength, ductility, and strength-ductility balance, the average area ratio of the ⁇ phase is preferably 20 to 80%.
• the average area ratio of the ⁇ phase is more preferably 30 to 70%, and even more preferably 40 to 60%.
• the average area ratio of the ordered phase is the average area ratio of metal structures other than the ⁇ phase. That is, in the metal structure, the remainder other than the ⁇ phase is an ordered phase.
• the average area ratio of the ⁇ phase is measured as follows.
• the L cross section (cross section cut along the rolling direction and thickness direction) and T cross section (cross section cut along the direction perpendicular to the rolling direction and along the thickness direction) of the steel plate are mirror polished.
• the mirror-polished surface is etched using a 10% aqueous oxalic acid solution to color the ⁇ phase white and the ordered phase gray. Thereby, a test piece with the polished surface as the observation surface is prepared.
• the average particle size of the ordered phase is 5.00 ⁇ m or more, the central part of the thickness of the cross section of the test piece is observed with an optical microscope at a magnification of 500 times. If the average particle size of the ordered phase is less than 5.00 ⁇ m, the central part of the thickness of the cross section of the test piece is observed with a scanning electron microscope at a magnification of 1000 times.
• the area ratio of the ⁇ phase is calculated. The area ratio of each ⁇ phase is calculated for a total of 10 views including 5 views of the L cross section and 5 views of the T cross section of the steel plate, and the arithmetic average value thereof is taken as the average area ratio of the ⁇ phase.
• the measurement of the area ratio of the ⁇ phase is carried out by preparing a test piece with the vertical and cross sections as observation surfaces instead of the L and T cross sections. do. If the steel material is a steel wire or steel bar, the part to be observed with an optical microscope shall be the part corresponding to the center of the diameter of the steel wire or steel bar in the cross section of the test piece. If the steel material is a steel pipe, the part to be observed with an optical microscope shall be the center of the thickness of the cross section of the test piece. Further, when the steel material is a steel strip, a section steel, or a foil, the measurement of the area ratio of the ⁇ phase is carried out in the same manner as when the steel material is a steel plate.
• the ordered phases include a B2 type ordered phase whose basic chemical composition is FeSi and a DO3 type ordered phase whose basic chemical composition is Fe 3 Si.
• the DO3-type ordered phase is superior in improving the balance between high strength and strength-ductility. Therefore, it is preferable to increase the proportion of the DO3 type ordered phase.
• the ordered phase includes a DO3-type ordered phase, and that the ratio of the DO3-type ordered phase to all ordered phases, determined by X-ray diffraction, satisfies the following formula B.
• the lower limit of the "[DO3 type ordered phase]/[all ordered phases]" value (hereinafter also referred to as "B value”) is more preferably 0.25, and still more preferably 0.30.
• the upper limit of the B value in Formula B is preferably 1.00, more preferably 0.91.
• the ratio of Fe atoms to Si atoms is completely 1/ It is not limited to 1, but includes cases in the range of 1/0.3 to 1/1.3, and even in the DO3 type ordered phase, the ratio of Fe atoms to Si atoms (Fe atoms/Si atoms) is completely 3. /1, but includes cases in the range of 3/0.5 to 3/1.4.
• the final annealing temperature is preferably 600 to 1150°C
• the cooling rate after final annealing is preferably 0.010 to 10.000°C/s.
• the annealing temperature is the surface temperature of the steel material.
• the cooling rate after final annealing is the average cooling rate obtained by dividing the temperature difference between the final annealing temperature and 400°C by the time required for cooling from the final annealing temperature to 400°C.
• the type of ordered phase and the ratio of the DO3 type ordered phase (B value of formula B) is measured as follows when the steel material is a steel plate.
• the type of ordered phase and the ratio of the DO3 type ordered phase are measured by XRD (X-ray diffraction method).
• the conditions for X-ray diffraction are as follows: CoK ⁇ rays are used as characteristic X-rays, voltage is 30 kV, and current is 100 mA.
• the X-ray diffraction measurement range is 10° ⁇ 2 ⁇ 110°, the step is 0.04°, and the integration time is 2 s, and XRD measurement is performed by the ⁇ -2 ⁇ method.
• XRD X-ray diffraction
• the ratio of the DO3 type ordered phase that is, the B value of formula B ([DO3 type ordered phase]/[all ordered phases]) is calculated from data measured by XRD.
• the B value of formula B is calculated by measuring the 2 ⁇ range of 10 to 110 degrees using CoK ⁇ radiation and processing the obtained information in the following manner.
• To calculate the B value of formula B a method is used in which the measured X-ray integrated intensity and intensity ratio are converted into the diffraction intensity of a specific lattice plane, and the phase ratio is determined from the average of the sums.
• DO3 type Fe 3 Si (220) and B2 type FeSi (210) are selected as specific diffraction surfaces.
• DO3 type Fe 3 Si ( 220) into the integrated intensity.
• B2 type FeSi the integrated intensity of the nine diffraction planes (110) (111) (200) (210) (211) (311) (023) (123) (400) is the integral of B2 type FeSi (210). Convert to strength.
• the numerical value in parentheses is the Miller index (hkl) of the crystal.
• the B value of Equation B is calculated from the following equation. Specifically, it is as follows.
• I B2 and I DO3 are calculated by substituting the integrated intensity and intensity ratio of the diffraction surface into the following equations.
• I B2 (hkl) is the measured integrated intensity
• R B2 (hkl) is the intensity ratio when R B2 (210) is set to 1
• I DO3 (hkl) is the measured integrated intensity
• R DO3 (hkl) is the intensity ratio when R DO3 (220) is set to 1
• B value of formula B I DO3 / (I B2 + I DO3 )
• the type of ordered phase and the ratio of the DO3 type ordered phase are measured by polishing the surface of the steel wire or steel bar from the radial direction to half the diameter of the steel wire or steel bar. A test piece to be used as an observation surface is prepared and carried out.
• the type of ordered phase and the ratio of the DO3 type ordered phase can be measured by preparing a test piece with the surface polished from the radial direction of the steel pipe until it is half the thickness of the steel pipe as the observation surface. and implement it.
• the steel material is a steel strip, a section steel, or a foil
• the type of ordered phase and the ratio of the DO3 type ordered phase are measured in the same manner as when the steel material is a steel plate.
• Both the B2 type ordered phase and the DO3 type ordered phase are ordered phases in which the ⁇ phase is ordered, and it is preferable that a large amount of Si, which is an ⁇ phase stabilizing element, is distributed in the ordered phase. Further, Si is an element effective in improving corrosion resistance, and it is preferable to distribute more Si, which is effective in improving corrosion resistance, in the ordered phase that becomes an anode preferential to the ⁇ phase in a corrosion reaction. Specifically, it is preferable that the average chemical composition of the ordered phase satisfies the following formula C.
• the ordered phase becomes a preferential anode over the ⁇ phase, but this behavior is more pronounced when the ordered phase contains less Ni and Cu, and becomes more pronounced when the ordered phase contains more Si and Al. .
• Ni and Cu be small, and that Si and Al be large.
• a larger amount of Si in the ordered phase is preferred since it improves the corrosion resistance of the ordered phase itself.
• Equation C is an equation showing these relationships. Therefore, when the average chemical composition of the ordered phase satisfies the following formula C, corrosion resistance is further improved.
• the lower limit of the "(Si ordered + Al ordered ) / (Ni ordered + Cu ordered )" value (hereinafter also referred to as "C value") is more preferably 0.29, and still more preferably 0.39.
• the upper limit of the C value in formula C is more preferably 0.98, and still more preferably 0.88.
• the final annealing temperature and the soaking time at the final annealing temperature are preferably 600 to 1150°C, and the soaking time at the final annealing temperature preferably satisfies the following formula 1.
• the diffusion and movement of atoms between the ordered phase and the ⁇ phase is sufficiently achieved, so that the average chemical composition of the ordered phase satisfies formula C.
• t indicates soaking time (sec) and T indicates final annealing temperature (°C).
• the soaking time is the time from when the target final annealing temperature is reached until the start of cooling.
• the average chemical composition of the ⁇ phase affects the ductility and strength-ductility balance, and is preferably an average chemical composition of the ⁇ phase that does not impair the ductility and strength-ductility balance. Specifically, it is preferable that the average chemical composition of the ⁇ phase satisfies the following formula D. When the average chemical composition of the ⁇ phase satisfies the following formula D, the ductility and strength-ductility balance of the ⁇ phase can be further improved, and the ductility and strength-ductility balance of the steel material itself can be improved.
• each element symbol ⁇ indicates the content of the corresponding element in the ⁇ phase (mass% ).
• the lower limit of the "Ni ⁇ +0.65Cr ⁇ +1.1Mn ⁇ +0.4Si ⁇ +13C ⁇ " value (hereinafter also referred to as "D value”) is more preferably 18.7, and still more preferably 22. It is 2.
• the upper limit of the D value in Formula D is preferably 39.5, more preferably 37.0.
• the final annealing temperature is preferably 600 to 1150°C
• the soaking time at the final annealing temperature preferably satisfies the following two equations.
• atoms are sufficiently diffused and moved between the ordered phase and the ⁇ phase, so that the average chemical composition of the ⁇ phase satisfies the D formula. 2 formula: 500 ⁇ t 0.5 /T ⁇ 1.77 (In formula 2, t represents the soaking time (sec) and T represents the final annealing temperature (°C).)
• ⁇ Average chemical composition of ⁇ phase and ordered phase When the steel material is a steel plate, the average chemical composition of the ⁇ phase and the ordered phase is measured as follows. A test piece is obtained by mirror polishing the L cross section and T cross section of the steel plate.
• the central part of the thickness of the steel plate cross section was examined with a scanning electron microscope at a magnification of 1000 times when the average grain size of the ordered phase was 5.00 ⁇ m or more, and when the average grain size of the ordered phase was less than 5.00 ⁇ m
• the sample is observed at a magnification of 2000 times
• elemental analysis is performed using an EPMA (Electron Probe Micro Analyzer) attached to a scanning electron microscope, and the average chemical composition of the ⁇ phase and ordered phase is measured.
• EPMA Electro Probe Micro Analyzer
• Analysis of the average chemical composition of the ordered phase is performed as follows. Using an enlarged image of the observation plane magnified 3000 times, a surface analysis is performed in a 30 ⁇ m ⁇ 30 ⁇ m area to identify the ordered phase. At this time, ordered phases having an average crystal grain size of 0.5 ⁇ m or more are targeted for identification. From the identified ordered phases, select 10 ordered phases in descending order of grain size, and analyze the chemical components of these 10 ordered phases at the center of the crystal grain (the center in the direction of the maximum diameter of the crystal grain) using the EPMA method. .
• the elements to be measured by the EPMA method are those shown in the average chemical composition of the steel material of the present disclosure.
• the mass % of each element to be measured in the ordered phase is determined. Substitute the mass % of the target element in the 10 ordered phases to be measured into the C value of the C formula ((Si ordered + Al ordered )/(Ni ordered + Cu ordered )), and calculate the arithmetic average of the C value of each C formula. Then, the representative value of the C value of the C formula for each visual field was calculated.
• This operation was performed for a total of 10 fields of view, 5 fields of L cross section and 5 fields of view of T cross section, and the representative value of the C value of the C formula obtained in each field was further arithmetic averaged by the number of fields, and the obtained value was The arithmetic average value of all the values was taken as the representative value of the C value of the C formula of the steel plate.
• the analysis of the average chemical composition of the ⁇ phase is carried out in the same manner as the analysis of the average chemical composition of the ordered phase, except that the target phase is the ⁇ phase instead of the ordered phase. Thereby, the mass % of each element to be measured in the ⁇ phase is determined, and a representative value of the D value of the D formula is obtained.
• the average chemical composition of the ⁇ phase and ordered phase can be measured by using a test piece whose longitudinal and cross sections are the observation planes instead of the L and T sections. Create and implement. If the steel material is a steel wire or steel bar, the part to be observed with a scanning electron microscope shall be the part corresponding to the center of the diameter of the steel wire or steel bar in the cross section of the test piece. If the steel material is a steel pipe, the part to be observed with a scanning electron microscope shall be the center of the thickness of the cross section of the specimen. Further, when the steel material is a steel strip, a section steel, or a foil, the measurement of the average chemical composition of the ⁇ phase and the ordered phase is carried out in the same manner as when the steel material is a steel plate.
• the ordered phase is a harder phase than the ⁇ phase, and its properties affect the strength of the steel material.
• the average grain size of the ordered phase it is possible to further improve the strength of the steel material.
• the average crystal grain size of the ordered phase is preferably 10.00 ⁇ m or less, more preferably 8.00 ⁇ m or less, and even more preferably 5.00 ⁇ m or less.
• the lower limit of the average crystal grain size of the ordered phase is, for example, 0.50 ⁇ m from the viewpoint of feasibility of manufacturing conditions.
• the intermediate annealing temperature, the final annealing temperature, the soaking time at the final annealing temperature, and the degree of cold working are determined.
• the degree of cold working is preferably 10% or more
• the intermediate annealing temperature and the final annealing temperature are preferably 600°C to 1000°C
• the soaking time at the final annealing temperature is the following 3. It is preferable that the formula -1 is satisfied.
• the following formula 3-1 is satisfied, crystal grain growth can be suppressed within an appropriate range, so that the average crystal grain size of the ordered phase becomes 10 ⁇ m or less.
• Formula 3-1 (t ⁇ T) 0.5 ⁇ 106 (In formula 3-1, t represents the soaking time for final annealing (sec), and T represents the final annealing temperature (°C).)
• the degree of cold working (%) is defined by the formula: ((Cross-sectional area of the material before processing) - (Cross-sectional area of the material after processing)) / (Cross-sectional area of the material before processing) x 100. Ru.
• the degree of cold working means, for example, when the steel material is a steel plate, the cold rolling rate, and when the steel material is a steel wire, the cold wire drawing rate.
• the average grain size of the ordered phase is measured as follows. After mirror-polishing the L and T cross sections of the steel plate, they are etched using a 10% aqueous oxalic acid solution to color the ⁇ phase white and the ordered phase gray. Thereby, a test piece with the polished surface as the observation surface is prepared. Observe a total of 10 fields of view, including 5 or more fields of view of the L cross section of the steel plate and 5 fields of view of the T cross section. Then, the image was observed at 500x magnification using an optical microscope and 1000x magnification using a scanning electron microscope.
• the average particle size of the ordered phase was 5.00 ⁇ m or more, the image observed at 500x magnification using an optical microscope was adopted. However, when the average particle size of the ordered phase was less than 5.00 ⁇ m, an image observed with a scanning electron microscope at a magnification of 1000 times was used. Using the adopted image, the crystal grain size of the ordered phase in each field of view is calculated by the straight test line cutting method described in JIS G 0551:2020. Then, in 10 visual fields, the arithmetic mean value of the calculated crystal grain sizes of the regular phase was calculated, and this value was taken as the average crystal grain size of the steel material.
• the average crystal grain size of the ordered phase can be measured by preparing a test piece with the longitudinal and cross sections as the observation planes instead of the L and T cross sections. ,implement. If the steel material is a steel wire or steel bar, the part to be observed with an optical microscope or scanning electron microscope shall be the part corresponding to the center of the diameter of the steel wire or steel bar in the cross section of the test piece. If the steel material is a steel pipe, the part to be observed with an optical microscope or scanning electron microscope shall be the center of the thickness of the cross section of the test piece. Further, when the steel material is a steel strip, a section steel, or a foil, the average crystal grain size of the ordered phase is measured in the same manner as when the steel material is a steel plate.
• the ordered phase is a B2-type ordered phase or a DO3-type ordered phase
• the area in the ordered phase that is a preferential anode, especially near the anti-phase boundary becomes a selective anode.
• the bonding force between metal atoms such as Fe, which form an ordered phase, and Si atoms is strong, so metal atoms such as Fe are difficult to ionize, resulting in better corrosion resistance.
• the anti-phase boundary which serves as a selective anode, has excellent corrosion resistance, the corrosion resistance of the steel material itself is further improved, and the formation of a passive film containing Si oxide, which has excellent corrosion resistance, is also promoted. Therefore, it is preferable to include an antiphase boundary in the ordered phase. More specifically, it is preferable to include one or more antiphase boundaries in one ordered phase.
• the term "opposite phase boundary" means a boundary in which the phase of the arrangement of atoms in the regular phase is shifted by 180 degrees (half period).
• the final annealing temperature is preferably 600 to 990°C
• the relationship between the final annealing temperature, the soaking time at the final annealing temperature, and the average grain size of the ordered phase after the final annealing is expressed by the following 4 formula. It is preferable to satisfy the following. When the following four formulas are satisfied, lattice defects such as dislocations that are the source of formation of the ordered phase are sufficiently introduced into the ordered phase, so that an antiphase boundary is formed in the ordered phase.
• Formula 4 8 ⁇ 10 ⁇ 3 ⁇ (T ⁇ t) 0.5 ⁇ d (In formula 4, t is the soaking time (sec), T is the final annealing temperature (°C), and d is the average crystal grain size of the ordered phase after final annealing.)
• ⁇ Presence or absence of anti-phase boundary in ordered phase If the steel material is a steel plate, the presence or absence of an antiphase boundary in the ordered phase is confirmed as follows.
• the presence or absence of anti-phase boundaries in the ordered phase is determined using a transmission electron microscope.
• a test piece (diameter 3 mm) is prepared using the thin film method with a thickness of 500 nanometers or less at the observation position as the observation surface.
• Observation with a transmission electron microscope was performed in an orientation in which DO3 type Fe 3 Si was observed from the ⁇ 002 ⁇ plane. Observation is performed at observation magnifications of 40,000 times, 80,000 times, and 400,000 times in each field of view, making a total of 10 fields of view.
• An ordered phase with an average crystal grain size of 0.5 ⁇ m or more is specified as a measurement target, and 10 of the specified ordered phases are selected in order from the largest grain size, and 40,000 times and 80,000 times of the 10 are selected. If one or more anti-phase boundaries are confirmed in one or more ordered phases at any magnification of , 400,000 times, there is an "anti-phase boundary in an ordered phase", and there is an anti-phase boundary in 10 ordered phases. If no boundary is confirmed, it is determined that there is no "opposite phase boundary in the regular phase.”
• the presence or absence of an antiphase boundary in the ordered phase can be confirmed by polishing the cross section until the thickness is 100 micrometers or less, and then electropolishing the observed position.
• a test piece (diameter 3 mm) with a polished surface having a thickness of 500 nanometers or less as an observation surface is prepared and tested.
• the steel material is a steel strip, a section steel, or a foil
• the measurement of the area ratio of the ⁇ phase is carried out in the same manner as when the steel material is a steel plate.
• the product of tensile strength and total elongation of the steel material of the present disclosure is preferably 30,000 MPa% or more, more preferably 50,000 MPa% or more.
• the tensile strength of the steel material of the present disclosure is preferably 1250 MPa or more, more preferably 1500 MPa or more.
• the total elongation of the steel material of the present disclosure is preferably 24% or more, more preferably 33% or more.
• the steel material is a steel wire, steel bar, or steel pipe
• the tensile strength and total elongation are measured by preparing a test piece cut so that the longitudinal direction is parallel to the stress axis.
• the steel material is a steel strip, section steel, or foil
• the tensile strength and total elongation are measured in the same manner as when the steel material is a steel plate.
• a method for producing a steel material of the present disclosure includes a step of hot working (hot rolling, hot wire drawing, etc.) a steel piece having the average chemical composition of the steel material of the present disclosure to obtain a processed material;
• a manufacturing method comprising the steps of annealing a workpiece, cold working the annealed workpiece (cold rolling, cold wire drawing, etc.), and final annealing the cold worked workpiece.
• the hot rolled sheet may be used as it is without cold working and final annealing.
• the hot working is performed at a heating temperature of 900 to 1150° C., for example.
• a hot-worked material it may be annealed, for example, in an air atmosphere, at a soaking temperature of 600 to 1150°C, and a soaking time of 1 to 1200 seconds.
• the cold working is performed, for example, by cold rolling at room temperature in an atmospheric atmosphere. Cold working may be performed multiple times, and intermediate annealing may be performed between multiple cold workings.
• the final annealing may be performed, for example, in an air atmosphere at a soaking temperature of 600 to 1,250° C. and a soaking time of 1 to 50,000 seconds. After final annealing, descaling, temper rolling, or shape correction using a tension leveler may be performed as necessary.
• a steel material having a metal structure containing a ⁇ phase and an ordered phase can be obtained by processing a steel billet having the average chemical composition of the steel material of the present disclosure.
• the method for manufacturing the steel material of the present disclosure includes performing hot rolling as the hot working and cold rolling as the cold working to produce the steel sheet, steel strip, or foil. Or manufacture foil.
• the steel material is a steel wire or a steel bar
• the method for manufacturing the steel material of the present disclosure performs hot wire drawing as the hot working and cold wire drawing as the cold working to manufacture the steel wire or the steel bar.
• the steel material is a welded steel pipe
• the method for manufacturing the steel material of the present disclosure includes performing hot rolling as hot working and cold rolling as cold working to obtain a steel plate or steel strip, and then producing the steel plate or steel strip. It is formed into a tubular shape to produce steel pipes.
• the method for manufacturing the steel material of the present disclosure performs hot rolling as the hot working and cold drawing as the cold working to manufacture the seamless steel pipe.
• Examples of the steel material of the present disclosure include steel plates, steel strips, steel wires, steel bars, steel sections, steel pipes, foils, and the like.
• the steel material of the present disclosure can be suitably applied to automobile parts that require high strength, high ductility, and high strength-ductility balance, as well as high corrosion resistance and high manufacturability, at a level that exceeds the current third generation AHSS.
• Example 35 was a hot-rolled plate that was not subjected to cold rolling or final annealing of the cold-rolled plate.
• tensile strength was used as an indicator of strength
• total elongation was used as an indicator of ductility
• product of tensile strength and total elongation was used as an indicator of strength-ductility balance.
• the mechanical properties were judged to be good if the tensile strength (TS) was 900 MPa or more, the total elongation (EL) was 22.0% or more, and the strength-ductility balance (TS ⁇ EL) was 19800 MPa ⁇ % or more.
• Corrosion resistance was evaluated using two methods.
• the first method for evaluating corrosion resistance is to perform the SST (salt spray test) test described in JIS Z 2371:2015, and after the test, remove corrosion products using the method described in JIS Z 2371:2015. After removal, external appearance observation, corrosion weight loss calculation, and steel dimension measurement are performed. The presence or absence of pitting corrosion is confirmed by external observation, and the corrosion rate is calculated from the corrosion weight loss, steel material density, and steel material dimensions.
• a (Excellent) if pitting corrosion with a diameter of 20 ⁇ m or more is not confirmed and the corrosion rate is 0.1 mm/year or less; pitting corrosion with a diameter of 20 ⁇ m or more is confirmed but the corrosion rate is 0.1 mm/year or less
• B (Good) if the diameter is 20 ⁇ m or more
• C (Good) if the corrosion rate is 0.1 mm/year or more and 0.5 mm/year or less
• pitting corrosion with a diameter of 20 ⁇ m or more was not confirmed.
• the second corrosion resistance evaluation method was the pitting potential measurement method described in JIS G 0577:2014.
• the test solution was a 3.5 mass% sodium chloride aqueous solution, and other measurement conditions were as described in JIS G 0577:2014.
• Pitting corrosion potential V' C 100 mV vs. It was measured in units of SSE, and the corrosion resistance was evaluated based on its size. In addition, when pitting corrosion did not occur even when polarized above the oxygen evolution potential, it was evaluated as "no pitting corrosion". Further, even if pitting corrosion occurs, if the pitting potential is 400 mV or more, it is judged that the material has corrosion resistance.
• the area to be investigated was a surface area of 1 m x 1 m or more including the edges of the steel material. Those in which no cracks or flaws with a length of 3 mm or more were observed were evaluated as "A (excellent).” In addition, if cracks or flaws are confirmed, but the maximum length is 3 mm or more and 5 mm or less, it is rated "B (good)", and if the maximum length is 5 mm or more and 8 mm or less, it is rated "C (fair)”. Those whose maximum length exceeded 8 mm were evaluated as "D (unacceptable)”.
• Table 3 shows the results of each survey.
• the notation "NO” in the ⁇ phase column means “no ⁇ phase”
• the notation "NO” in the ordered phase column means “no ordered phase”.
• the steel material of the disclosed example has high strength, high ductility, and high strength-ductility balance, and has high corrosion resistance at a level exceeding the current third generation AHSS, compared to the steel material of the comparative example. I understand. Furthermore, it can be seen that the steel materials of the disclosed examples have suppressed cracks or flaws and have excellent manufacturability.
• FIG. 1 shows an optical micrograph (500x magnification, white part is ⁇ phase, gray part is regular phase) of the metal structure of the steel material of the present disclosure example of test number 35 after hot rolling annealing and before finish annealing. show.
• an example of an optical micrograph of the metal structure of the steel material of the disclosed example of test number 36 (500x magnification, white part is ⁇ phase, gray part is regular phase) is shown in FIG. 2.
• FIGS. 1 and 2 it can be seen that the steel material of the example of the present disclosure is completely different from the metal structure of the prior art. It can also be seen that the metal structure is refined by cold working and final annealing.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)

Priority Applications (7)

Applications Claiming Priority (1)

Publications (1)

Family

ID=90099045

Family Applications (1)

Country Status (7)

Citations (4)

Family Cites Families (2)

• 2022
  • 2022-09-02 CN CN202280099565.2A patent/CN119768548A/zh active Pending
  • 2022-09-02 KR KR1020257008510A patent/KR20250049398A/ko active Pending
  • 2022-09-02 US US19/106,224 patent/US20260062774A1/en active Pending
  • 2022-09-02 EP EP22957471.0A patent/EP4582564A4/en active Pending
  • 2022-09-02 WO PCT/JP2022/033178 patent/WO2024047877A1/ja not_active Ceased
  • 2022-09-02 JP JP2024543754A patent/JPWO2024047877A1/ja active Pending
• 2025
  • 2025-02-27 MX MX2025002473A patent/MX2025002473A/es unknown

Patent Citations (4)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events